JERUSALEM: A letter penned by legendary physicist Albert Einstein discussing one of his groundbreaking theories was sold in Jerusalem on Tuesday for over $100,000 as part of trove of documents that went under the hammer.The handwritten missive, sent in 1928 by Einstein from Berlin to a mathematician about the formalisation of the “Third Stage of the Theory of Relativity”, was snapped up by an anonymous buyer for $103,700 (83,600 euros).